zimbra.bmpZimbra, the San Mateo open-source messaging software start-up that has been on a roll lately, now lets you work with it offline.

Among companies offering AJAX technology for email/office products — which let you do cool useful things like scroll over an address and have a map pop up, and switch seamlessly to your contacts and calendar — Zimbra is the first to be available both online and offline, to our knowledge. Google has said it will make its products available offline, but hasn’t followed through yet.

It lets you use your browser offline, and includes the ability to search and organize, respond to emails, etc. Once you get online again, your emails are sent. Until now, people using Zimbra offline would have to switch back to their basic Outlook, and then switch back to Zimbra when they came online again.

Both POP accounts and RSS feed folders are synced to, which is useful, and makes us want to get the product when the consumer version is out by the end of the year — to be downloadable from the site.